Iron ceramic pigment



United States Patent 3,166,430 IRON CERAMIC PIGMENT Clarence A.Seahright, Lakewood, Ohio, assignor to The Harsh-aw Chemical Company,Cleveland, Ohio, a corporation of Ohio N0 Drawing. Filed Feb. 27, 1964,Ser. No. 347,952 14 Claims. (Cl. 106-299) This application is acontinuation-in-part ofcopending application Serial No. 157,852, filedDecember 7, 1961,

which is in turn a continuation-in-part of application Serial No.110,223, filed May 15, 1961, which in turn is a continuation-in-part ofapplication Serial No. 28,457, filed May 11, 1960, all now abandoned.

This invention relates to an iron-containing zircon pigrnent and moreparticularly to a coral colored ceramic pigment comprising zircon(zirconium silicate) having iron contained in the zircon crystallattice.

The present invention is characterized as the calcination product ofzirconium oxide, silicon oxide and iron oxide in the presence offluoride ions. The proper-ties of this product are such that it may beused uniquely as a coloring agent in glazes. The instant ceramicpigments or coloring agents are stable in most glazes imparting a pinkto coral hue thereto.

Broadly, the compositions of the present invention comprise zirconhaving from about 0.25 percent to about 6 percent by Weight of iron asiron oxide in the lattice. Essentially, the pigment composition containsfrom about 30 percent to about 80 percent by weight zirconium oxide,from about 15 percent to about 55 percent by weight silicon oxide andfrom about. 0.25 percent to about 25 percent by weight of iron oxide,associated together to the extent of at lea-st 40 percent of said oxidesin the form of the iron-containing zircon crystal lattice.

The fact that the pigments of the present invention may be used ascoloring agents in glazes is completely unexpected in view of the factthat compositions having identical component ingredients prepared in adifferent manner fail to act as coloring agents in glazes. Compositionsprepared by calcining mixtures of zircon (zirconium silicate) and ironoxide in the presence of fluoride ions produce only the pale yellow orivory color characteristic of iron oxide in glaze when the zircon-ironpigment is used in normal amounts (e.g., amounts used for coloringenamels and the like). If excessive amounts are used in tion pattern forzircon.

a glaze, the glaze becomes a brownish red color complete- 1y devoid ofpink which is also characteristic of iron oxide when used alone.

This theory seems to be borne out by the fact that iron oxide itself cannot be used as a coloring agent for glazes to produce pink or coral huesand that iron-containing ceramic pigments comprising a host lattice orcolor fixing agent which is not as inert as zircon are not stable inglazes. Examples of such pigments include the reaction product of ironoxide and silica or its natural counterpart, Jap Ochre. i

The zircon which is present as part of the pigments of the presentinvention is a zirconium silicate produced during the calcination and isof the same structure (as shown by X-ray dilfraction) as the naturallyoccurring mineral zircon. Optimum proportions are approximately those ofa product wherein all the zirc'onia and silica would be converted tozircon and with the maximum iron oxide contained in the zircon lattice.Less favorable proportion-s, however, can be used and can give goodresults, varying from the best to only fair. The zirconium dioxide(zirconia) and silicon dioxide (silica) react to form zircon, any excessof either remaining unreacted. The portion of the calcination productindicated by X-ray diffraction to have the zircon pattern is referred toherein as the reacted portion. A greater or lesser amount of iron oxideis held in the zircon crystal lattice depending upon the conditions ofpreparation. Usually the calcination product, even after grinding andwashing, contains some iron oxide not fixed in the zircon crystallattice and may show a characteristic X-ray diffraction pattern for ironoxide (iron in the zircon lattice does not show as iron oxide in anX-ray diffraction pattern).

Proportions of the component ingredients are easily chosen by thoseskilled in the art which will give a product 40 percent to percent, ormore, of reacted material (zircon) determined by the characteristicX-ray diflrac- In addition to zircon having iron in its lattice,mixtures containing unreacted ingredients of the batch with the reactedmaterials may be used advantageously as ceramic colors or pigments.

In carrying out the process of this invention, it is im-' portant thatthere is a source of fluoride ions included in the calcination batchalong with the source of zirconium oxide, silicon oxide and iron oxide.ferred form the precalcination mixtures of the present invention includea source of alkali metal ions. Preferably, the source of fluoride ionmay be an alkali metal fluoride, or silicofluoride or an alkali metalfluoride plus a different halide such as alkali metal chloride orbromide. The iron compound may be dissolved in water and then mixed withthe zirconia, silica, and halide and preferably alkali components toform a damp mass. The mass is calcined, powdered in a suitable manner,such as by ball milling, washed free of soluble salts and then dried.The calcination preferably is carried out in a closed sagger, or underequivalent conditions, which provides calcination of the batchsubstantially in contact with its own vapors and, incidentally,substantially out of contact with air. C-alcination may be for a periodof about one-half hour to about eight hours at temperatures in the rangeof 700 C. to 1300 C., the optimum calcination conditions being from 800C. to 1100 C. for a period of about three to six hours.

The product resulting from the calcination contains at least 40 percentby weight and preferably at least 80 percent by weight of zircon (asdetermined by the X-ray diflraction data) based on the entire weight ofthe pigment product. X-ray analysis of raw calcination batches has shownthat substantially no zircon was present. X-ray analysis of the pigmentproducts produced by calcination of such batches has shown quantities ofabove 40 percent by weight, usually above 80 percent by weight of zirconto be present. While the strongly colored pigments containing in excess'of 80 percent zircon are preferred, Weaker pigments such as thosepigments containing as little as 40 percent zircon have some value.

As mentioned above, the mineralizer compounds of this invention requireat least fluoride ions and in some cases preferably also alkali metal.ions and/or different halide ions. The halide ions may be derived fromthe compounds of zirconium or compounds of iron present in thecalcination mixture, or the ions may be derived from compounds speciallyplaced in-the calcination mixture as a source of one or more ions. Themineralizer compounds should be present in the calcination mixture inamounts such that from about 0.25 percent to about 12 percent by weightof fluoride ions are present and preferably from about 0.25 percent toabout 8.0 percent by Moreover in its pre-' weight of alkali metalionsare present, based; on the combined weights of the silica, zirconia andferric oxide in the calcined pigment. The preferred proportions ofmineralizer compounds are such that about 0.25. percent by weight toabout 8 percent by weight of alkali metal ions arepjrese'nt, from about0.25 percent by weight to about 12 percent by weight of fluoride ionsare present, and

up to about 8.0 percent by weight of halide ions other 5 than fluorideions are. present. 5

The silicon compound which may be silicon dioxide or a compound capableof yielding silicon dioxide is present in the calcination mixture intherange of from about 15'percent by weight to about 55 percent byweight, expressed as SiO (preferably 24 percent to 45 percent), and, forexample, maybe silicon dioxide or s-ilicic acid. The zirconium compoundwhich may be zirconium dioxide or a compound capable of yieldingzirconium oxide 25 percent by weight'of the calcination mixtureexpressed as ferric oxide (F6203), preferably 3 percent to 15 percentand may be a compound such as, for instance, ferric chloride, ferroussulfate, ferrous ammonium sulfate, ferric oxide, or ferric nitrate. Asindicated hereinbefore the important aspect of the present invention isthe iron being contained in the crystal lattice of the zircon. Broadlythe invention includes pigments having as much iron contained in. thezircon lattice as possible but amounts greater than about 6 percent donot appear possible. Moreover it is extremely diificult to obtainpigments having more than about 3 percent by weight in the lattice basedon the weight of the zircon. In order to obtain pigments having optimumcoloring properties at'least 0.5 percent iron should be present in thelattice.

The source of alkali metal ions may be a compound such as, for instance,sodium chloride, sodium fluoride, sodium bromide, sodium carbonate,sodium silicofluoride, postassium chloride or lithium chloride. Thesource of fluoride ions may be a fluoride compound such as, forinstance, sodium fluoride, potassium fluoride, cryolite, sodiumsilicofluoride, zirconium oxyfluoride, and the source of the halide ionsother than fluoride, ions may be a halogen compound such as, forinstance, zirconium oxychloride, sodium chloride, sodium bromide, orpotassium chloride, The halide ion other than fluoride ion is optional.

As a further refinement of the present invention the,

pigments are leached or treated with an acid. This treatment removes theunreacted iron oxide not trapped in the zircon lattice. Such treatedpigments have been found to give improved colors which are cleaner andmore pinkish in color than the untreated pigments. After treatmentthe-pigments may have as much as 24 percent iron oxide removed andusually have about 6 percent to 10 percent iron oxide removed. Howeverthe treated pigments of the present inventionalways contain iron, atleast 0.25 percent and preferably at least about 0.5 percent, thusindicating that the remaining iron is trapped or otherwise tied up bythe zircon.

Moreover, the fact that the treated pigments, having only the minimalamounts of iron impart better color to ceramic glazes than the samepigment untreated, defilLl'tClY indicates that functional portion of theiron oxide is trapped by the zircon. Other zircon pigments containingamounts of iron similar to the pigments of the present invention butprepared differently do not color a ceramic glaze a pinkish coral withor without treatment with an acid.

' Ferric Chloride Sodium Bromide.

Examples of calcinatiion batchmixtures for the preparation of theceramic pigments of this invention are set forth in the following table,designated as Table I. The units for the component ingredients set forthin Table I are parts by weight.

TABLE I ABODEFVVGH Zirconium Dioxide Silica Ferric Oxide FerrousSulfate.

Ferrous Ammonium Sulfate Sodium Fluoride Sodium Ohloride Cryolite(Na A1F15 Specific examples of the preparation of the pigment of this inventionare as follows:

Example I Example II 6 grams of ferric chloride were dissolved in waterand mixed with 4 grams of potassium chloride, 3 grams of sodiumfluoride, 31 grams of silica, and 63 grams of zirconium oxide to form adamp mass. The damp mass was then calcined in a covered inert sagger atabout 850 C. The calcine was then ground in a ball mill, washed free ofsoluble salts, and dried. The resulting product was a strong brown redceramic pigment which yielded a desirable coral pink color ina glaze.

Example 111 10 grams of ferrous sulfate were dissolved in water andmixed with 4 grams of sodium chloride, 3 grams of sodium fluoride, 31grams of silica and 63 grams of zircon-free zirconium oxide to form adamp mass. The damp mass was then calcined ina covered inert sagger atabout 850 C. for a period of about one hour. The calcine was then groundin a ball mill, washed free of soluble salts and dried. Theresultingproduct, which was found to contain about 50 percent of syntheticzircon, was a brown red ceramic pigment which yielded a coral pink colorin a glaze.

' Example IV 20 grams of ferrous sulfate were dissolved in water andmixed with 7.5 grams of sodium chloride, 6 grams of sodium fluoride, 31grams of silica and 63 grams of zirconfree zirconium oxide to form adampmass. The damp mass was then calcined in a'covered inert sagger atabout 850 C. for a period of about three hours. The calcine was thenground in a ball mill, washed free of soluble salts and dried. Theresulting product, which was found to contain about percent of syntheticzircon, was a strong brown red ceramic pigment which yielded a desirablecoral pink color in the glaze.

Example V v salts and. dried. The result was a violet brown ceramicpigment which yielded a coral pink color in glaze.

Example VI 6 Each of the pigments of Examples VII through XXI is mixedinto a typical Cone 5 tile glaze, using 10 parts pigment to 100 partsglaze.

1345 parts of Opax 91% zirconia; 7% silica; and the Composition of Cone5 tile glaze: 1 Parts y weight remainder alumina and titania), 855 partsof silica, 180 5 Q P parts of iron oxide and 180 parts of bariumfluoride were Wi a) 12 intimately mixed and calcined in a covered inertsagger slllca 19 at 1050 C. for six hours. The calcine was then mixed y(Edgar Pl kaollll) 15 With 40 percent Water and 0.50 percent bariumhydrate, Barlllmfafbonate qs) 6 charged into a ball mill and ground forsix hours. After 10 Lead 1915111011? 2)2] 17 drying, the material waspassed through a hammermill. Magneslum carbonate s) 2 The pigment wasbrown red in color. Each composition was then fired on ceramic tiles atabout In accordance with the present invention, further ex- 1130 C. togive vitreousglaze coatings having varying amples, relating to thepreparation of the pigments are shades of coral, ranging from a faintpink to a deep pinkset forth in the following Tables II and III. 5 ishred hue.

TABLE II Constituents, Parts by Weight VII VIII IX X XI XII XIII XIV XVXVI XVII XVIII XIX XX XXI Zirconia (ZIOz) 56.8 54.2 54.2 12.3 13.2 13.513.9 14.3 50 51.3 52.6 54.0 55.5 Opax (91% zirconia; 7% silica;

and the remainder alumina and titania) 57.3 57.3 39.3 40.3 41.9 43.044.2 Silica (SiOz) 27.9 27.1 27.1 24.6 26.7 24.4 25.0 25.7 26.4 27.225.5 26.3 27.0 27.3 Ferric Oxide (O. K. Williams R-l599) .3 5 3.1 5 62.9 12.5 10.3 7.9 5.4 2.3 Ferric Oxide (F3209, Mapico 5 EG-3 9.1 FerricOxide (F3103, Mapico EG-SO)- 9.2 Ferric Oxide (F8203, Mapico 297) 9.34.7 Ferrous Sulphate (F6SO4-7H2O)- 9.0 Zircon (zror-sioz) 1.4 1.4 SodiumFluoride (NaF) 2.7 3.3 3.9 4.1 4.2 4.3 Sodium Chloride (NaCl)- 3.6Cryolite (NaeAlFt) 3.1 3.1 5.3 3.3 Sodium silicofiuoride (NmSiF 3.0 2.46.4 6.6 5.7 6.9 7.1 3.75 9.0 9.2 9.5 9.7 China clay (Kaolin)- 3. 75' 3.34.0 4.1 4.2

Caloination Temperature, De-

gree Centigrade 350 1,050 1, 050 1,050 1,050 1,050 1, 050 1, 050 1,0501, 050 1,050 1, 050 1, 050 1, 050 1, 050

After the above constituents or ingredients were mixed In order tocompare the pigments of the present invenand calcined in accordance withthe procedures outlined tion with iron-containing zirconia-silicacompositions of in Examples I through VI, ceramic pigments were obtheprior art the following examples are set forth:

tamed which produced the characteristic pink coral hue E l A in a glaze.Each pigment was calculated to have the xamp e composition as set forthin Table III, wherein each pig- C stit nt Parts by weight ment isidentified by the same example number used to Zirconia (ZrO 500designate the starting materials set forth in Table I Ferric oxide (Fe OThe oxide content of each raw mix or composition for Flu 92 each pigmentis based on the assumptions that Pota sium feldspar, 35.82%

(1) All of the alkali metal salts are washed out, Sodium nitrate, (2)All of the halides or halogen compounds are removed Q 9- byvolatilization and/or Washing, 50 B9116 (3) All of the silicontetrafluoride (SiF is removed by Z1110 Q 191% volatilization, andCIYOllIe, 10.48% V i A11 Sulfur, oxldes formed are rammed by VolatlhzaThe above constituents were intimately mixed and caltlon or Washmgcinedat a temperature of about 950 C. for three hours. *Moreover where thefixed iron content exceeded 2 per- A light brown stain was obtained.When this stain was cent ferric oxide the unreacted zirconia and silicaconstitmixed with the above Cone 5 glaze composition in proporuentscomprised less than about 7 7 percent of the pigment tions of 10 partsstain to parts glaze, and fired .on

.TABLE III 5 w vII VIII IX X I XI XII I XIII I XIV XV XVI XVII XVIII IXIX XX IXXI Oxide Content Calculated for Raw Composition of Table IIParts-By Weight 55.2 52.0 56.1 48.6 49.9 51.2 52.6 54.0 50.0 51.3 52.654.0 55.5 27.5 23.6 31.1 27.1 27.7 23.5 29.3 30.2 26.6 27.3 23.1 23.329.6 2.0 1.5 1.3 10.3 0.3 0.3 0.3 0.3 1.5 1.5 1.6 1.6 1.7 9.2 9.3 4.712.3 10.5 3.1 5.6 2.9 12.5 10.3 7.9 5.4 2.3 Titania- 0.5 0.5 0.3 0.3 0.30.3 0.3

Iron Oxide ggglleelgtgl Oalcined Percent By Weight Ferric Oxide (totalcalculated) 3.0 9.3 9.3 10.1 5.2 14.4 11.3 9.2 6.4 V 3.3 13.3 11.4 3.36.0 3.1 Ferric Oxide (total analyzed)--- 3.4 9.4 9.6 9.7 4.85 FixedFerric Oxide after acid 1eaching analyzed 1 0 1.5 0 6 2.15 1.03 2.7 2.52.0 1.4 1.0 2.36 2.6 2.2 1.9 1.6

1 This amount of iron oxide is a measure of the iron oxide content inthe 2irconinm silicate crystal lattice. The iron oxide was analyzed to!each pigment after it had been boiled in 20% hydrochloric acid, using100 grams of dry ground pigment per 200 milliliters of the acid.

7 ceramic tiles at 1130 C., the stain was destroyed and only an ivorycolored glaze was obtained.

Example B Repeating Example A by substituting cryolite for the flux, thesame results were obtained. The light brown stain failed to producesignificant color in the glaze demonstrating that the stain wasdestroyed.

Example C When one-third of the-zirconium oxide of Example A wasreplaced by silica in Example A, an ivory glaze was obtained using Opaxas the source of zirconia and a light,

brownish glaze was obtained using pure zirconia.

Neither of the glazes appeared to have a pink color.

The following Example D sets forth preparation of a pigment compositionaccording to the process of the present invention deviating onlyslightly from the above Examples A through C. g

Example D color imparted to the glaze was decidedly pink. The fact' thata pink color was imparted to the glaze clearly shows this pigment to bediiferent in kind from the pigments prepared in Examples A through Cwhere absolutely no pink could be detected in a glaze containing thepigments of these examples. Moreover, by contrast, it appears that theborax and boric acid of the above flux are deleterious to the pigmentsof the present invention.

The ceramic colors or pigments of the present invention by themselves donot always appear to have a pinkish coral color, but when mixed withglazes act to produce a vitreous glazed surface on tile having acharacteristic coral color which is definitely pink. Moreover incoloring glazes, the pigment is often referred to as a pink coralpigment even though the pigment itself may not be coral in color. Manytimes these pigments which do not appear to have a coral color impart apinkish coral color to glazes. Moreover the pigments of the presentinvention have become known as -a class to'those skilled in the art andwhen referred to as coral pigments it is generally understood that theclass is referred to rather than the color. The expression coralpigments has acquired a secondary meaning.

The pigments prepared according to my present inven tion may be used forcoloring other ceramic materials, such as underglazes, vitreous enamelsand may be used withv various organic vehicles such as for example inthe production of paints and the like.

While specific examples of the invention have been set forthhereinabove, it is not intended that the invention be limited solelythereto but to include all of the variations and modifications fallingwithin the scope of the appended claims.

What is claimed is:

1. A coral'pink'ceramic pigment composition consisting essentially offrom about 30 percent to about 80 percent by weight of oxide ofzirconium, from about 15 percent to about 55 pencent by Weight of oxideof silicon and from about 0.25 percent to about 25 percent by "weight ofoxideof iron, associated together to the extent of at least about 40percent of said oxides by weight in the form of an iron-containingzircon crystal lattice having at least about 0.25 percent by weight ironoxide contained in said lattice. i

'2. The pigment of claim 1 wherein at least about 80 percent by weightof said oxides are associated together in the form of an iron-containingzircon crystal lattice having from about 0.25 percent to about 6 percent' iron oxide contained in said lattice.

3. A coral pink ceramic pigment composition consisting essentially offrom about 30 percent to about percent by weight of oxide of zirconium,from about 15 percent to about 55 percent by weight of oxide of siliconand from about 0.25 pencent to about 25 percent by weight of oxide ofiron, associated together to the extent of at least about 40 percent ofsaid oxides by weight in the form of an iron-containing zircon crystallattice having from about 0.25 percent to about 6 percent by weight ironoxide within said lattice.

4. The pigment of claim 3 wherein at least about 80 percent by weight ofsaid oxides are associated together in the form of an iron-containingzircon crystal lattice having from about 0.5 percent to about 3 percentiron oxide contained in said lattice.

5. A coral pink ceramic pigment consisting essentially of from about 48percent to about 70 percent by weight of oxide of zirconium, from about24 percent to about 45 percent by weight of oxide of silicon, and fromabout 3 percent to about 15 percent by weight of oxide of iron, saidoxides being associated together to the extent of at least about 40percent by Weight in the form of an ironcontaining zirconia-silicacrystal lattice having from about 0.25 percent to about 6 percent ironoxide contained in said lattice.

6. The pigment of claim 5 wherein at least about 80 percent by weight ofsaid oxides is present in the form of an iron-containing zirconia-silicacrystal lattice having from about 0.5 percent to about 3 percent ironoxide contained in said lattice.

7. As a new composition of matter a precalcination mixture containingcompounds capable of yielding silica, zirconia, ferric oxide andfluoride ions upon calcination and wherein the proportions ofsuchcompounds are adjusted so as to yield on calcination a compositioncomprising from about 15 percent to about 55 percent by weight silica,from about 30 percent to about 80 percent by weight zirconia and fromabout 0.25 percent by weight to about 25 percent by weight ferric oxideand from about 0.25 percent to about 12 percent fluoride ions based onthe combined weights of said silica, zirconia and iron oxide.

8. As a new composition of matter a calcination mixture which issuitable for the preparation of coral pink ceramic pigments bycalcination consisting essentially of from about 15 percent by weight toabout 55 percent by weight, expressed as SiO of a silicon compoundcapable of yield-ing silicon oxide; from about 30 percent by weight toabout 80 percent by weight, expressed as ZrO of a zirconium compoundcapable of yielding zirconium oxide;

from about 0.25 percent by weight to about 25 percent by weight,expressed as Fe O of an iron compound capable of yielding Fe O and afluorine containing compound capable of yielding from about 0.25 percentby Weight to about 12 percent by weight of fluoride ions.

9. The composition of matter of claim 8 wherein there is present acompound capable of yielding from about 0.25 percent by weight to about8.0 percent by weight of alkali metal ions based on the combined Weightsof silica, zirconia and ferric oxide.

10. As a new composition of matter a calcination mixture which issuitable for the preparation of coral pink ceramic pigments bycalcination consisting essentially of from about 15 percent by weight toabout55 percent by weight, expressed as SiO of a silicon compoundcapable of yielding silicon oxide; from about 30 percent by weight toabout 80 percent by weight, expressed as ZrO of a zirconium compoundcapable of yielding zirconium oxide;

.from about 0.25 percent by weight to about 25 percent are present, fromabout 0.25 percent by Weight to about 8.0 percent by weight of alkalimetal ions are present, and from about 0.25 percent by weight to about8.0 percent by weight of halide ions selected from the group consistingof chloride ions and bromide ions are present.

11. A method of preparing an iron-zirconia stain comprising calcining ata temperature in the range of from about 700 C. to about 1300 C. anadmixture containing compounds of zirconium capable of yieldingzirconium oxide to the extent of from about 30 percent to about 80percent by weight, compounds of silicon capable of yielding siliconoxide tO'thfi extent of from about 15 percent to about 55 percentbyweight, compounds :of iron capable of yielding iron oxide to theextent of from about 0.25 percent to about 25 percent by weight, andmineralizer capable of supplying alkali metal ions and fluoride ions.

12. The method of claim 11 wherein the compounds about 80 percent byweight, compounds of silicon capable of yielding silicon oxide to theextent of from about 15 percent to about 55 percent by Weight, compoundsof iron capable of yielding iron oxide to the extent of from about 0.25percent to about 25 percent by weight, a source of alkali metal ions, asource of fluoride ions, and min- ,eralizer present comprising from 0.25percent to 12 percent by weight of fluoride ion and from about 0.25percent to about 8 percent of alkali metal ion.

14. The method of claim 13 wherein the compounds of iron capable ofyielding iron oxide are water-soluble salts of iron.

References Cited by the Examiner UNITED STATES PATENTS 1,719,432 7/29Kinzie 10648 2,441,447 5/48 Seabright 106299 3,046,150 7/62 Jamieson106-499 OTHER REFERENCES Meilor: Comprehensive Treatise on Inorganic andTheoretical Chemistry, vol. 7, pages 98 and 99.

TOBIAS E. LEVOW, Primary Exam ner.

1. A CORAL PINK CERAMIC PIGMENT COMPOSITION CONSISTING ESSENTIALLY OFFROM ABOUT 30 PERCENT TO ABOUT 80 PERCENT BY WEIGHT OF OXIDE OFZIRCONIUM, FROM ABOUT 1K PERCENT TO ABOUT 55 PERCENT BY WEIGHT OF OXIDEOF SILICON AND FROM ABOUT 0.25 PERCENT TO ABOUT 25 PERCENT BY WEIGHT OFOXIDE OF IRON, ASSOCIATED TOGETHER TO THE EXTENT OF AT LEAST ABOUT 40PERCENT OF SAID OXIDES BY WEIGHT IN THE FORM OF AN IRON-CONTAININGZIRCON CRYSTALS LATTICE HAVING AT LEAST ABOUT 0.25 PERCENT BY WEIGHTIRON OXIDE CONTAINED IN SAID LATTICE.